The Japanese archipelago, which stretches in the north-south direction from North Latitude 26deg to 45deg, has a large variation in climate from subtropical to frigid. This large variation in climate is reflected in a large diversity in heat­ ing requirements; no heating is needed on the islands of Okinawa, to the very south, while the annual heating degree day (D18-18) from Honshu to Hokkaido ranges from 1,400 to almost 5,000. This is comparable to the difference be­ tween Rome and Moscow. Except for Hokkaido, the sum­ mer in Japan is one of high temperatures and high humidity. In midsummer, humid days with temperatures soaring over 30 °C continue for long periods in many regions of Japan.